Shenyue Xu

Low energy (e, 2e) study from the 1t(2) orbital of CH4.

Single ionization of the methane (CH(4)) 1t(2) orbital by 54 eV electron impact has been studied experimentally and theoretically. The measured triple differential cross sections cover nearly a 4π solid angle for the emission of low energy electrons and a range of projectile scattering angles. Experimental data are compared with theoretical calculations from the distorted wave Born approximation and the molecular three-body distorted wave models. It is found that theory can give a proper description of the main features of experimental cross section only at smaller scattering angles. For larger scattering angles, significant discrepancies between experiment and theory are observed. The importance of the strength of nuclear scattering from the H-nuclei was theoretically tested by reducing the distance between the carbon nuclei and the hydrogen nuclei and improved agreement with experiment was found for both the scattering plane and the perpendicular plane.

An (e, 2e + ion) investigation of dissociative ionization of methane.

We present in this paper an (e, 2e + ion) investigation of the dissociative ionization of methane by 54 eV electron impact employing the advanced reaction microscope. By measuring two electrons and the ion in the final state in triple coincidence, the species of the ions are identified and the energies deposited into the target are determined. The species and the kinetic energies of the fragmented ion show strong dependence on the intermediate states of the parent ion. Possible decay pathways for the production of different species of ions are analyzed.

Electron impact dissociative ionization of methane: Formation of protons

Production of protons from dissociative ionization of methane by electron impact is investigated using the reaction microscope. By the triple coincidence measurement of all the three charged particles in the final state, we found that the (2a1)−1(npt2)1, (2a1)−1, (1t2)−2(3a1)1 and (2a1)−2(3a1)1 states of the intermediate CH4+ give major contributions to the formation of protons, and each state dissociates in a different mechanism.

An (e, 2e + ion) investigation of fragmentation of methane induced by low energy electrons

An (e, 2e+ion) investigation of the ionization and dissociation of methane by 54 eV electron impact is performed using the advanced reaction microscope. By measuring two electrons and the ion in the final state in triple coincidence, the species of the ions are identified, and the energies deposited into the target are determined. The species and the kinetic energies of the fragmented ion show strong dependence on the intermediate states of the parent ion.

Electron impact induced break-up of aligned H2: molecular frame (e, 2e) studies

Break-up of molecular hydrogen (H2) by 54 eV electron impact induced dissociative ionization is investigated. The alignment of the H2 molecule is determined by the post-collision dissociation process. Therefore, fully differential cross sections for fixed in space molecular axis were measured. Thus the most detailed dynamical features of electron molecule collisions are obtained to perform benchmark tests of theory.

Imaging the electrons from transfer ionization collisions

The electrons emitted into the continuum in transfer ionization of He2+ on helium collisions in the energy range of 75 – 400 keV were imaged using reaction microscope. The electron emission patterns show big difference for projectile velocity lower and upper than 1 a.u. in the present studies.

A GaAs photoemission electron source combined with a Reaction Microscope

Negative electron affinity GaAs photoemission electron sources are the electron sources of choice in many applications. We have built a GaAs photoemission source to be used in a reaction microscope for near threshold and kinematically complete experiments [1]. In this study, we present the current status of the photoelectron source, a precise characterization of the electron beam and first results of electron-atom scattering experiments.

Electron emitted in transfer ionization in He2+ on helium collisions

A complete experiment for He2+ on helium collisions was performed over a relatively broad energy range by using a reaction microscope in Lanzhou in order to clarify the emission properties. In the experiment the momenta of recoil ions, the emitted electron, and the charge state of the scattered projectiles were recorded in coincidence in event-by-event mode. By reconstruction of the momentum vector of electrons, the momentum distributions of the continuum electrons in the scattering plane were obtained. The distributions show characteristics of the electrons originated from transfer ionization in the collisions.

Differential investigations of charge transfer processes in low energy ion-atom/molecule collisions

The progress of differential studies of ion-atom/molecule collisions using the reaction microscope was reported. The state-selective and angular differential cross sections were measured for slow ion-atom collisions. In this paper we focus on the two-electron processes, namely double electron capture and transfer ionization, occurring in the collisions of ion impact on two-electron target system of helium and molecular hydrogen, respectively. The molecule Coulomb explosions were investigated by employing the negative ion characteristic. The transfer momentum dependence of two-electron processes for He2+ and H+ impact on He and H2 were compared, and the kinetic energy release in Coulomb explosions induced by He2+ and H+ was measured.